Receiver functions using OBS data: promises and limitations from numerical modelling and examples from the Cascadia Initiative

Abstract

SUMMARYThe expanding fleet of broadband ocean-bottom seismograph (OBS) stations is facilitating the study of the structure and seismicity of oceanic plates at regional scales. For continental studies, an important tool to characterize continental crust and mantle structure is the analysis of teleseismic P receiver functions. In the oceans, however, receiver functions potentially suffer from several limiting factors that are unique to ocean sites and plate structures. In this study we model receiver functions for a variety of oceanic lithospheric structures to investigate the possibilities and limitations of receiver functions using OBS data. Several potentially contaminating effects are examined, including pressure reverberations from the water column for various ocean-floor depths and the effects of a layer of low-velocity marine sediments. These modelling results indicate that receiver functions from OBS data are difficult to interpret in the presence of marine sediments, but shallow-water sites in subduction zone forearcs may be suitable for constraining various crustal elements around the locked megathrust fault. We propose using a complementary approach based on transfer function modelling combined with a grid search approach that bypasses receiver functions altogether and estimates model properties directly from minimally processed waveforms. Using real data examples from the Cascadia Initiative, we show how receiver and transfer functions can be used to infer seismic properties of the oceanic plate in both shallow (Cascadia forearc) and deep (Juan de Fuca Ridge) ocean settings.

Structure of the oceanic lithosphere and upper mantle north of the Gloria Fault in the eastern mid‐Atlantic by receiver function analysis

“…These effects are also visible in the raw data in Figure d and are probably related to signal and ambient noise‐induced reverberations in the sedimentary cover at each station [ Hannemann et al , ]. The interpretation of RFs can be hampered by the presence of such reverberations and must therefore be done carefully [ Audet , ; Kawakatsu and Abe , ]. Furthermore, the ZRT coordinates are preferred for the calculation of RFs at OBSs, as the usage of the ray‐oriented coordinate system (LQT) may lead to a large amplitude at 0 s on the Q component of the LQ RFs in the presence of sediment reverberations [e.g., Olugboji et al , ], which cannot be modeled by using a 1‐D velocity‐depth model.…”

“…Thickened or thinned oceanic crust may be related to overthrusting, underplating, or basin formation. The RF phase of the Moho arrives only 1 or 2 s after the dominant P phase [e.g., Kawakatsu et al , ] and therefore requires high‐frequency data [ Audet , ], and a good signal‐to‐noise ratio (SNR). Furthermore, it is often masked by sediment reverberations which hamper a direct interpretation of the Moho signal [ Audet , ; Kawakatsu and Abe , ].…”

Comment on “Nature of the Seismic Lithosphere‐Asthenosphere Boundary within Normal Oceanic Mantle from High‐Resolution Receiver Functions” by Olugboji et al.

“…The significance of sediment layer (and also water layer) reverberations in seismic observation in the ocean is well recognized, and it has been one of the most challenging factors that hamper investigating deeper crustal and mantle structures [e.g., Godin and Chapman , ; Zeldenrust and Stephen , ; Ball et al ., ; Ruan et al ., ; Bell et al ., ; Abe and Kawakatsu , ; Audet , ]. Olugboji et al .…”

Reply to comment by Kawakatsu and Abe on “Nature of the seismic lithosphere‐asthenosphere boundary within normal oceanic mantle from high‐resolution receiver functions”

“…Unlike land stations, applying standard receiver function analysis to ocean bottom stations poses unique challenges due to the presence of unwanted noise or shallow-layer signals which can obscure the crust and mantle signature that is of primary interest to the seismologist [e.g., Audet, 2016]. These challenges include the presence of large amplitude infragravity waves and ocean-current-induced tilt noise [e.g., Crawford et al, 1991;Webb, 1998;Willoughby and Edwards, 2000] as well as sediment and water column reverberations [Godin and Chapman, 1999;Harmon et al, 2007].…”

“…We tested oceanic lithosphere models with a shallow low-velocity sediment layer to examine reverberation behavior in simple 1-D models, similar to those examined by Audet [2016].…”